The present invention relates to a temperature sensing switch which may be associated with, for example, a compressor included in an air conditioning system of a motor vehicle.
A compressor of an automotive air conditioning system, for example, is apt to seize when heated beyond a certain temperature level during operation due to shortage of refrigerant or like cause. To eliminate this, there have been proposed systems which upon elevation of compressor temperature above such a level stop the operation of the compressor to thereby protect it from seizure, as disclosed in Japenese Utility Model Laid-Open Publication No. 55-130087/1980 (referred to as former prior art hereinafter), for example. Meanwhile, when the compressor is cooled below a certain temperature sucking liquid refrigerant therein, the liquid becomes compressed to damage valves and other structural elements of the compressor. Deactivating a compressor for protection against cooling beyond the critical temperature is described in, for example, Japenese Utility Model Laid-Open Publication No. 56-127390/1981 (referred to as latter prior art hereinafter).
The former prior art uses a bimetallic strip for sensing compressor temperature and the latter prior art, a PTC thermistor. It may readily be contemplated in view of the former prior art to actuate a movable contact of a contact mechanism by use of a temperature-sensitive member which is made of a shape memorizing alloy. However, the implementation taught by the former prior art is responsive only to excessive rise of compressor temperature, and that taught by the latter prior art only to excessive drop of the same. That is, it is impossible to sense both the excessive rise and excessive drop of temperature without resorting to two independent temperature sensing sections and, hence, without making the switch arrangement bulky. A compact design of such a switch would minimize a space required for installation and promote the ease of electrical wiring.